Abstract. Periodontitis is a highly prevalent condition characterized by a bacterial infection of periodontal tissues. The development of improved, non-invasive treatments for periodontitis could have implications for public health in the United States and worldwide. Calprotectin (S100A8/A9) is an antimicrobial protein that is expressed in the cytoplasm of gingival epithelial cells and polymorphonuclear leukocytes. In a murine model of periodontitis, S100A8/A9 slows the progression of periodontitis and reduces alveolar bone loss. We hypothesize that efficient delivery and expression of calprotectin-specific mRNA in vivo will lead to reduced inflammation and slow the progression of periodontitis. Herein, we propose a novel method to treat periodontitis using topical delivery of an mRNA construct encoding calprotectin. We will demonstrate that food- safe, polymeric gene delivery vehicles can topically deliver the therapeutic mRNA in vivo. To firmly establish this approach, polyelectrolyte complexes (polyplexes) with mRNA will be characterized using dynamic light scattering, zeta potential, and ethidium bromide (EtBr) dye exclusion. Optimization of polyplex uptake and message translation will be quantified by expression of a GFP reporter gene using fluorescence microscopy and flow cytometry. To increase biological persistence of the polyplexes complex and promote healing of infected tissue, we will develop a cellulosic hydrogel bandage. The hydrogel will be characterized using spinning disk rheology, and tensile testing. Polyplex loading into and release from the hydrogel will also be quantified using fluorescence measurements or labeled polyplexes. Once ideal delivery conditions are optimized, the effects of modified calprotectin expression will be assessed using a murine model for periodontitis with and without endogenous calprotectin expression. The impact of calprotectin expression on inflammation and alveolar bone loss will be quantified using flow cytometry and microCT measurements. Use of the polyplex-loaded hydrogel bandages are expected to improve transfection efficiency, increase calprotectin-dependent antimicrobial activity, and reduce the signs of experimental periodontitis in our mouse model. If successful, this project has the capacity to provide clinicians with improved tools to treat periodontitis, and improve understanding of topical gene delivery and the biology of periodontitis.